The light source of the projector generally emits light of high brightness by using a lamp of a discharge system. However, when the discharge of electrons between electrodes of the lamp is continued for a long time, a locus of the discharge becomes unstable and a flicker is generated in a projected image. Therefore, there is a light source driving device having a function for stabilizing the locus of the discharge and preventing the flicker by performing an operation for periodically supplying a normal electric current and a large electric current in comparison with the normal electric current on the side of the light source driving device for supplying electric power to the lamp and lighting (operating) the lamp (see patent literature 1 (FIG. 4)). Otherwise, it is also considered that a large electric current is flowed in comparison with the initial stage of the period (see patent literature 2 (FIGS. 3 to 6)).
Further, in the projector, a method for calculating a focus position by picking-up the image of a test pattern projected to a screen by a monitor camera, and detecting a high crest value of the amplitude of a horizontal signal of this picked-up photographing image (image data) is proposed as an auto focus method of the projected image (see patent literature 3).    [Patent literature 1] JP-T-10-501919    [Patent literature 2] JP-T-2002-532867    [Patent literature 3] JP-A-2000-241874